It was the largest postage stamp the United States had issued up to that time. Its design was 1.80 by 1.05 inches, and its overall size was 1 61/64 by 1 15/64 inches, making it 50 percent larger than conventional U.S. commemoratives. (These so-called "jumbo" dimensions later were used for several commemorative stamps issued in the early 1970s.)

It wasn't until July 9, 1969, a week before Apollo 11 was launched, that Postmaster General Winton M. Blount disclosed plans for the stamp and attendant details. On that date, Blount announced that "Apollo 11 will mark America's first mail run to the Moon." In a public-relations masterstroke credited to Julian Scheer, NASA's assistant administrator for public affairs, Blount revealed that the astronauts would take with them the engraved die that later would be used to make the stamp's printing plates, along with a special "Moon letter" bearing a die proof of the stamp. The letter would be personally postmarked by Armstrong and Aldrin while they were on the Moon, Blount said.

But how could the designer Paul Calle be sure his picture, which had to be completed a month before the launch of Apollo 11, would be accurate?

NASA provided photographs or duplicates of all the equipment that would be involved in the landing, including a lunar module which Calle viewed at the plant of the manufacturer, the Grumman Corporation. In addition, Calle knew that Armstrong would put his left foot down first as he came off the module's own, padded "foot"; that was choreographed in advance.

What he didn't know - what no one knew - was whether the landing area would be solid or powdery, and, if it was the latter, how deep the module would sink. The artist took a chance and showed the module's tripod foot making a barely perceptible imprint. Fortunately, that turned out to be exactly what happened.

On July 20 1969, at 40 seconds after 4:17 p.m., Eastern Daylight time, the lunar module Eagle landed on the Moon, carrying Armstrong and Aldrin. Collins remained in the Columbia command module orbiting overhead.

As the world watched and listened via television and radio, Apollo 11 Commander Armstrong sent the good news from 235,000 miles away: "Houston, Tranquility Base here. The Eagle has landed." (Listen to Armstrong's transmission here... )

Later that same day, at 20 seconds after 10:56 p.m. EDT, Armstrong descended a ladder, stepped off the lunar module's footed to the Moon's surface and radioed his famous message: "That's one small step for man, one giant leap for mankind."

Aldrin later joined Armstrong on the Moon's surface. As it turned out, the two astronauts found themselves too busy with scientific and other duties to carry out the assignment of postmarking the "Moon letter." So the envelope and its die proof actually were given the "MOON LANDING/USA/JUL/20/1969" hand stamp during the return journey.